1. Field of the Invention
The present invention relates to an image forming apparatus for fixing, by heating, an image formed on a sheet-like recording medium thereto with sublimating ink.
2. Description of the Related Art
An exemplary conventional technique relating to the above field of art is disclosed in Japanese patent application xe2x80x9cKokaixe2x80x9d No: Hei. 10-297197. According to this, a metal substrate includes a coloring ground layer acting also as a rust-preventive layer, a transparent resin layer as an optical transparent resin layer formed over the coloring ground layer, the resin layer (made of e.g. porous alumina) being made of acrylic resin, polyester resin, urethane resin etc., and an inkjet receiving layer formed over the resin layer and made of e.g. porous alumina. After application of a sublimating ink or pigment on the inkjet receiving layer by an inkjet printing, the sublimating pigment is heated in a heating furnace or by a hot press, whereby the sublimating pigment in the inkjet receiving layer is sublimed into the transparent resin layer. Then, the inkjet receiving layer is removed to obtain an ornamental metal body having a colored pattern fixedly formed within the transparent resin layer (see, for example, paragraphs Nos. 0010-0013 and FIG. 4). This image forming art can be applied to a recording medium using, as a substrate thereof, metal material which is hardly deformed by heat. However, if this art is applied to a recording medium using, as a substrate thereof, e.g. resin material which is deformed significantly by heat, occurrence of thermal deformation in the substrate during the heating process, especially, xe2x80x9cwrinklesxe2x80x9d cannot be avoided.
Further, Japanese patent application xe2x80x9cKokaixe2x80x9d No: Hei. 10-16188 discloses an image forming apparatus. According to this, first, a primary image is formed on a thermal transfer sheet by e.g. an inkjet printer. Then, this thermal transfer sheet having the image formed thereon is laid over a recording sheet and these sheets are pressed and heated together by means of heat press rollers whose temperature is controlled, whereby the image (ink) formed on the thermal transfer sheet will be sublimed by the heat and transferred onto an ink fixing layer of the recording sheet (see, for example, paragraphs Nos. 0008-0012 and FIG. 1). In the case of this image forming technique, the surface temperature control of the heat fixing roller is strictly effected. However, since the contact between the heat press rollers and the recording sheet is substantially line contact, the surface of the recording sheet at the normal temperature (room temperature) is heated and pressed momentarily and then left to cool at the normal temperature again. Therefore, if material such as resin sensitive to heat is employed as the substrate of the recording sheet, wrinkles developed during the heating process will remain after the cooling.
According to further art disclosed by Japanese patent application xe2x80x9cKokaixe2x80x9d No: 2001-105638, sublimating ink is transferred from an ink ribbon onto a surface of a recording sheet. In order to heat and fix the ink on the sheet, the sheet is charged into a heater box, in which the sheet is advanced and heated between a press roller and a heat roller opposed to each other with a small gap therebetween or between a heat roll and a conveyer belt disposed along a portion of the peripheral face of the heat roll, and then the sheet is discharged by a transport roller from the heater box immediately (see, for example, paragraph Nos. 0039-0058 and FIG. 1). With this image forming technique, the recording sheet heated by the heating roller is immediately discharged from the heater box into the normal temperature. Therefore, if material such as resin sensitive to heat is employed as the substrate of the recording sheet, wrinkles developed during the heating process will remain after the cooling.
Further, though differing in the properties in the recording medium from the present invention, in the field of textile printing, according to an exemplary technique disclosed by Japanese patent application xe2x80x9cKokaixe2x80x9d No: Hei. 08-311782, in order to obtain a print of a graphic image of as clear definition as possible, printing is effected by means of the inkjet printing method on a textile whose wrinkles were smoothed out by smoothing out rolls. After printing, in order to reinforce the fixing of the dye and also to improve its color development, the textile is charged into a heater device to be heated therein. Then, the textile is discharged from the device immediately to be cooled at the normal temperature (see paragraphs Nos. 0041-0043, 0061-0070 and FIG. 2). This art, however, does not provide any means for removing xe2x80x9cwrinklesxe2x80x9d after completion of the heating process. Therefore, if this art is employed for a recording material of not textile but some heat-sensitive material such as resin, the wrinkles developed during the heating process will remain.
In view of the above, a primary object of the present invention is to provide an image forming apparatus usable for a recording material using a heat-sensitive material such as resin as the substrate thereof as the apparatus has a function for eliminating deformation developed in a recording medium during heating thereof by a heating fixing unit before cooling of the medium.
For accomplishing the above-noted object, according to the present invention, an image forming apparatus for fixing, by heating, an image formed on a sheet-like recording medium thereto with sublimating ink, the apparatus comprising:
a heating fixing unit for receiving and heating the recording medium and then discharging the heat-fixed recording medium, the heating fixing unit including a heating space for heating the recording medium and a transporting mechanism for transporting the medium in the heating space; and
a smoothing-out mechanism for discharging the recording medium from the heating space while smoothing out or flattening the recording medium.
With the above construction, according to the image forming apparatus of the invention, the recording medium printed with image with the sublimating ink is introduced into the heating space by the transporting mechanism, where the medium is exposed to a required heating process for stably fixing the image thereon. And, the resultant recording medium is automatically discharged from the heating space. In the course of this, when the recording medium is being discharged from the heating space, this medium retaining the heat received in the heating space, thus having sufficient plasticity is subjected to the function of the smoothing-out mechanism. Therefore, even if deformation has occurred during the heating for ink fixation or due to application of an external force during its transport, this deformed recording medium may be effectively smoothed out into the appropriate flat shape.
Preferably, the smoothing-out mechanism includes a curved transporting section for forcibly bending the recording medium discharged or being discharged from the heating space into a direction for bending the medium as viewed from its lateral side.
Namely, in this type of recording medium, there tend to develop wrinkles in the form of wave-like undulations in the cross section of the medium. Therefore, with the above-proposed construction, the recording medium is forcibly bent in the direction traversing such wave-like undulations, such that such type of wrinkles may be effectively eliminated or occurrence of such type of wrinkles may be avoided in advance.
Preferably, the curved transporting section is arranged in such a manner as to orient the image-formed face of the recording medium to the outer side. With this, when the recording medium is caused to pass the curved transporting section, a tension will occur on the outer face of the recording medium on which the image is formed and this tension serves to smooth out fine wrinkles on the surface of the medium.
Still preferably, the curved transporting section includes an angular member extending straight along the width direction of the recording medium, a guide mechanism for forcibly bending the recording medium by pressing the recording medium against the angular member, and a heating mechanism for heating the angular member.
With this construction, the width-wise entire area of the recording medium will be pressed at one time against a projecting portion of the angular member extending straight, so that the medium may be subjected to a uniform smoothing-out effect particularly in the width direction thereof. Further, this angular member is heated to a high temperature by the heating mechanism, the recording medium discharged from the heating space and having a gradually reducing temperature can be heated again for recover its thermal plasticity and processed under this condition. Consequently, the recording medium may be bent smoothly, thus realizing very effective smoothing out of the medium.
The angular member can be considered as a group of infinitely small and an infinite number of smoothing-out elements arranged straight along the main scanning direction. And, the recording medium being moved in the sub scanning direction by the transporting mechanism can be considered as being discharged while being uniformly smoothed out in the width direction thereof along and on these smoothing-out elements.
Preferably, the angular member is disposed downwardly of the recording medium to be discharged and the guide mechanism includes a guide face which is inclined downward relative to a posture of the leading end of the discharged recording medium.
With this construction, the leading end of the recording medium discharged from the heating space of the heating fixing unit will be pressed against the inclined guide face to be oriented downward. Thus, the bending of the recording medium in the side view thereof may take place smoothly. Further, this bending will occur such that the transportation-wise downstream portion of the medium is bent downward, which bending direction agrees with the bending direction under the gravity, i.e. under the effect of the dead weight of the recording medium per se. Therefore, the recording medium bent by the curved transporting section can be effectively pressed against the corner of the angular portion with the help of the dead weight of the recording medium i.e. the gravity.
Preferably, downwardly of the guide face, there is provided a partitioning wall for forming an open space around the recording medium. With this, by maintaining the air temperature of this pace at a relatively high value, discharge of heat from the angular member or the exit of the heating space may be effectively restricted. At the same time, this can restrict rapid discharge of heat from the recording medium discharged from the heating space. Consequently, as the recording medium is guided with an appropriate posture thereof while the angular member of the inside of the heating space is maintained at the relatively high temperature, the smoothing-out operation on the recording medium can proceed effectively and appropriately.
Still preferably, the apparatus further comprises a stocker for receiving the recording medium discharged from the smoothing-out mechanism with a posture in which the leading end of the medium is inclined downward.
With this construction, even when the recording medium past the smoothing-out section is discharged in the form of being dropped or when an elongated medium is discharged continuously, the recording medium may be received by the stocker with the lower end of the medium being caused to slide on the inclined face of the stocker disposed below. Therefore, by guiding the recording medium along the inclination direction of the stocker, the medium can be collected compactly and smoothly.
Alternatively, the smoothing-out mechanism includes a press roller mechanism for pressing the recording medium discharged or being discharged from the heating space against a flat face.
With this, it become possible to apply the pressing force to the recording medium in a reliable manner, regardless of difference in the thickness of the recording medium. Adjustment of the pressing force is possible by e.g. attaching a weight to the roller. Needless to say, it will be also possible to apply a predetermined urging force to the roller by means of e.g. a spring. However, the construction utilizing a dead weight alone will be simpler and less costly. With this construction, any deformation such as wrinkles developed in the surface of the recording medium during the heating process by the heating fixing unit may be xe2x80x9cironed outxe2x80x9d by the effect of the press roller on the medium still having high temperature and associated plasticity at the last stage of the heating process. Hence, the deformation such as wrinkles may be eliminated before the medium is cooled. Therefore, such wrinkles will not remain in the final printed product after the cooling process.
Preferably, the press roller mechanism includes a stationary roller supported to be rotatable about a fixed horizontal shaft and a movable roller supported to be movable closer to and away from the peripheral face of the stationary roller, the movable roller being urged in the direction closer to the peripheral face.
With this construction, as the movable roller is movable closer to and away from the peripheral face of the stationary roller, the press roller mechanism can receive recording media of various thicknesses. Further, the press roller mechanism can receive also a recording medium having very large wrinkles in the thickness direction thereof. Further, as the movable roller is urged in the approaching direction, this roller can positively contribute to the smoothing of the deformation such as wrinkles.
Incidentally, the deformation such as wrinkles developed in the surface of the recording medium during the heating process at the heating fixing unit may be dissolved by e.g. the ironing effect of the press roller mechanism. However, if the recording medium is suddenly discharged from the heating fixing unit to the outside, resultant rapid cooling experienced by the recording medium from the temperature inside the heating space to the room temperature can lead to new occurrence of deformation such as wrinkles in the medium.
Then, the apparatus may further comprise a slow cooling mechanism disposed downstream of the smoothing-out mechanism in the transporting direction of the recording medium and adapted for slowly cooling the discharged recording medium to the normal temperature, and the slow cooling mechanism includes a guide member having a slide guiding face along which the recording medium is slid and a heater for controlling the temperature of the slide guide face to have a temperature gradient that the temperature of the slide guide face is lowered gradually along the transporting direction of the recording medium.
With the above construction, the recording medium which was heated at the heating fixing unit for heat fixation of the printed image is slowly returned from the ink fixing temperature (generally, 150xc2x0 C. or more) to the normal temperature (room temperature) by the slow cooling mechanism. As a result, occurrence of deformation such as wrinkles due to rapid cooling from the temperature inside the heating fixing unit (ink fixing temperature) to the normal temperature (room temperature) may be effectively restricted. Accordingly, there has been realized an image forming apparatus which can not only eliminate the wrinkles developed in the heating process, but also avoid further wrinkles which could occur during the cooling process.
Further and other features and advantages of the invention will become apparent upon reading the following detailed description of preferred embodiments thereof with reference to the accompanying drawings.